Error codes and out-parameters in C

The C convention: return success or failure, deliver the value through a pointer.

#include <stdlib.h>
#include <string.h>

int parse_pair(const char *text, int *first, int *second) {
    if (text == NULL || first == NULL || second == NULL) {
        return 0;
    }
    const char *comma = strchr(text, ',');
    if (comma == NULL) {
        return 0;
    }
    *first = atoi(text);
    *second = atoi(comma + 1);
    return 1;
}

int use_it(void) {
    int a = 0;
    int b = 0;
    if (!parse_pair("3,4", &a, &b)) {
        return -1;
    }
    return a * b;
}

How it works

1. Zero or negative for failure keeps the check uniform.
2. The out-parameter is only written on success.
3. Callers can then chain checks without nesting deeply.

Keywords and builtins used here

• NULL
• char
• const
• if
• int
• parse_pair
• return
• use_it
• void

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